On Thu, Mar 25, 2010 at 06:50:21PM +0900, KAMEZAWA Hiroyuki wrote: > On Thu, 25 Mar 2010 09:48:26 +0000 > Mel Gorman <mel@xxxxxxxxx> wrote: > > > > In that case, compact_finished() can't > > > find there is a free chunk and do more work. How about using a function like > > > free_pcppages_bulk(zone, pcp->batch, pcp); > > > to bypass pcp list and freeing pages at once ? > > > > > > > I think you mean to drain the PCP lists while compaction is happening > > but is it justified? It's potentially a lot of IPI calls just to check > > if compaction can finish a little earlier. If the pages on the PCP lists > > are making that much of a difference to high-order page availability, it > > implies that the zone is pretty full and it's likely that compaction was > > avoided and we direct reclaimed. > > > Ah, sorry for my short word again. I mean draining "local" pcp list because > a thread which run direct-compaction freed pages. IPI is not necessary and > overkill. > Ah, I see now. There are two places that pages get freed. release_freepages() at the end of compaction when it's too late for compact_finished() to be helped and within migration itself. Migration frees with either free_page() or more commonly put_page() with put_page() being the most frequently used. As free_page() is called on failure to migrate (rare), there is little help in changing it and I'd rather not modify how put_page() works. I could add a variant of drain_local_pages() that drains just the local PCP of a given zone before compact_finished() is called. The cost would be a doubling of the number of times zone->lock is taken to do the drain. Is it justified? It seems overkill to me to take the zone->lock just in case compaction can finish a little earlier. It feels like it would be adding a guaranteed cost for a potential saving. -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>